1. Field of the Invention
This invention relates to oil reservoir studies, and more particularly to a method of preparing a radioactive tracer material capable of partitioning between oil and water phases in a reservoir which is being studied.
The determination of the amount of oil in place in subterranean reservoirs has been a subject of great interest to the oil industry for many years. Such information is obviously of considerable interest in the case of a newly discovered reservoir which is to be produced, and is of even greater interest in a reservoir which has been subjected to primary production and possibly secondary production. In recent years the interest in tertiary oil recovery methods for recovering additional quantities of oil from reservoirs which have been subjected to primary and secondary production has increased. Since such tertiary oil recovery methods are quite expensive, it is important that a method be available for determining the amount of residual oil in a formation to be subjected to tertiary recovery prior to the initiation of the tertiary recovery operation. The residual oil present in reservoirs which have been subjected to primary or secondary recovery is oil which remains in place after waterflooding operations or the like. Such residual oil resists recovery by conventional methods, as it is trapped in the formation pores or otherwise retained in the formation by various mechanisms.
As a result of the increasing interest in the recovery of additional quantities of oil from oil reservoirs which have been subjected to secondary recovery operations, the oil industry has directed a continuing effort to the development of improved methods for determining the amount of residual oil in formations which have been subjected to secondary recovery.
2. Prior Art
There has been a great deal of work involving the use of radioactive tracers as reservoir evaluation tools. One procedure for determining the residual oil saturation of a previously waterflooded oil reservoir is described in U.S. Pat. No. 4,071,756. In that patent, a separate injection of a first water soluble tracer and a second radioactive tracer soluble in both oil and water is described. A series of gamma ray logs is carried out and the logging results are then interpreted to obtain an indication of the residual oil saturation in the reservoir. Several examples of tracer materials soluble in both oil and water are described in U.S. Pat. No. 4,071,756.
Method for preparing ethylene iodohydrin are described in CA93: 113945a (1980) and CA94: 102763j (1981).